1. Field of the Invention
The subject matter of this invention is related to network protectors, generally and bussing systems for network protectors, specifically.
2. Description of the Prior Art
Network protectors are known. A network protector is special kind of circuit breaker, it generally consists of an automatic electrically operated circuit breaker which includes a tripping mechanism, suitable control equipment and network relays. The entire operation of the protector is usually controlled by two relays; a master relay and a phasing relay. A third relay is sometimes required to provide against unnecessary protector operations due to regenerative loads or temporary surge currents.
Low voltage AC networks assure high service continuity and heavy load density in downtown areas, for example. In the low voltage networks, the secondary mains of transformers are connected together through the network and consumer services are supplied from these mains. Power is supplied to the network mains through network transformers and network protectors located at the junctions of the network mains in a grid or at major load points around a secondary loop. The network transformers are supplied from two or more primary feeders with adjacent transformers being connected to different feeders. When one feeder is out of operation, the load continues to be fed by transformers connected to the remaining primary feeds. Consequently, customers' service is supplied from at least two different directions. Services supplied from a transformer location have a minimum of three paths of supply. Because of these multi-paths for load currents, abrupt changes in load, such as motor starting currents, cause much less voltage disturbance then on a radial system. Network protectors are often designed to assure service continuity in 125/216 and 277/480 volt Y-connected secondary network systems. These are commonly used in high load densities as in metropolitan and suburban business districts.
Understanding the construction and use of network protectors maybe found in the following publications, which are also incorporated herein by reference: "Network Protectors type CM-22 for heavy load density areas", Descriptive Bulletin 35-550 published by the Westinghouse Electric Corporation, Switchgear Division, East Pittsburgh, Pa. dated March, 1964. "CMD Network Protector" Descriptive Bulletin 35-552 D WE A published by the Westinghouse Electric Corporation, Switchgear Division dated September 1997 and "Instruction for Type CMD-1875A Network Protectors" published by the Westinghouse Electric Corporation dated 1975.
Network protectors are often found in dust proof or moisture proof enclosures, which are often disposed in passageways and runs in underground utility systems in large metropolitan areas. In many cases the circuit breaker element of the network protector is a four-pole circuit breaker, whereas the external terminals of the entire network protector system for the loads are three-pole. It is thus necessary somewhere within the network protector system to provide a transition between a four-pole system and a three-pole system. Until now this has been accomplished within the circuit breaker element of the network protector system. There are certain disadvantages associated with this solution. Most circuit breakers are already densely packed, metal enclosed devices with little or no room for welded or bolted internal connections. Furthermore, it is time consuming and expensive to adapt four-pole circuit breaker systems to three-pole applications by making changes within the circuit breaker casing. It would be advantageous therefore if a way could be found to utilize a network protector system, which had a capability of interconnection with a four-pole breaker but which nevertheless did not have the disadvantage associated with making the transition between a four-pole system and a three-pole system within the circuit breaker casing per say.